THE GEOLOGICAL SECTIOX BETWEEX BFLAWAYO 

 AXD THE VICTORIA EALL8. 



By H. B. Mauik, B.A., 



Director, GeoJogiccd Surreij, S. HJuule.-'ia. 



]] itii ( >nc Fold III (/ Map 

 Read JuJn 15, 1920. 



The geological section exhibited has been compiled from 

 observations made on many different occasions. It follows 

 closely the line of railway running north-west from Bnlawayo 

 to the Yictoria Falls, the chief exceptions being an extension 

 to the south-east of the Matopo Hills and a straight line drawn 

 across country from Inyantue to Wankie, where the railway 

 makes a wide detour to the south-west. Also, in places where 

 the railway makes a considerable curve to obtain grade on 

 ascending- the basalt scarp bej^ond Nyamandhlovu and on 

 descending it approaching Sawmills, the section has been 

 shortened to give the scarps their due gTadient. It has been 

 possible to draw the section to scale through tlie courtesy of 

 the engineers of the Rhodesian Railways in supplying levels; 

 and to the same source and to Mr. A. J. C. Molyneux I am 

 indebted for information from wells and boreholes, wliich has 

 served to increase materially the accuracy of the tliickness of 

 the beds. (See folding map.) 



The section extends over a length of 282^ miles. The 

 liorizontal scale is 2i miles to the inch, and the vertical scale 

 500 feet to the inch, thus being* exaggerated over 26 times. 



Three formations are encountered along the course of the 

 section, apart from alluvia and residual soils. The oldest 

 formation is the crystalline schists with granite intrusions and 

 dolerite dykes ; the second formation is tlie sedimentary beds 

 of the Karroo system, and the youngest is the Kalahari sand. 



The oldest formation appears at the surface on two 

 portions of the section — first, on tlie high veld between 

 Bnlawayo and the Matopn Hills, and again between Dett and 

 Wankie. The first portion you will pass over on your journey 

 to the Matopo Hills. The crystalline schists consist of green- 

 stones and the banded ironstone or quartz-magnetite rock. 

 Both groups are strongly folded, and dip at liigh angles. Tlie 

 greenstones are metamorphosed basic ig'neous rocks, generally 

 hornblende-bearing rocks such as epidiorite and amphibolite. 

 Certain bands in them are vesicular or amygdaloidal, and other 

 portions show well-developed pillow structure. In parts of 

 the country, too, agglomerates and tuffs appear interbedded 

 with them. Tl'ere is little doubt that the greenstones repre- 

 sent in the main a succession of volcanic rocks. The horn- 

 blendic greenstones decompose to t]ie red clay soil wliicli you 



